Castor



FIG. 1 is a side view of a castor showing my new design;

FIG. 2 is a front view of the castor;

FIG. 3 is a plan view of the castor;

FIG. 4 is a perspective view of the castor;

FIG. 5 is an underneath plan view of the castor;

FIG. 6 is a side view of the castor in an alternative condition;

FIG. 7 is a front view of the castor in the alternative condition; and

FIG. 8 is a perspective view of the castor in the alternative condition.

The ornamental design for a castor, as shown and described.